1. Technical Field of the Invention
The present invention relates to a vehicle control system for performing real-time distributed control through a plurality of electronic control units on an in-vehicle network, and relates to the electronic control units used for the vehicle control system.
2. Related Art
In this type of vehicle control system, vehicle conditions, such as an amount of intake air, are monitored and converted to time-dependent data for transmission/reception between the plurality of electronic control units on an in-vehicle network. Various in-vehicle devices are thus subjected to distributed control in a synchronized manner based on such common time-dependent data. Therefore, in performing the distributed control of the in-vehicle devices under such a vehicle control system, it is important to adequately keep the freshness of the time-dependent data so as to adequately perform the distributed control.
As this type of vehicle control system, Japanese Patent Laid-Open No. 2005-199954, for example, discloses one in which the electronic control units on the in-vehicle network each administer the time (time stamp) of acquisition of the time-dependent data. Then, in performing the distributed control of the various in-vehicle devices, the freshness of the time-dependent data is evaluated by comparing the acquired time (time stamp) with the current time. Specifically, a determination is made as to the validity of the time-dependent data, and the apparatuses are adequately controlled according to the result of the determination, so that the adequacy of the distributed control can be ensured.
It is true that, in the conventional vehicle control system mentioned above, the adequacy of the distributed control is ensured through the determination process for the validity of the time-dependent data. However, depending on the operation conditions, such a conventional vehicle control system can significantly deteriorate the reliability of the determination on the validity.
The above conventional vehicle control system has been realized as a time-synchronization network system, in which the time of synchronization is typically expressed in a form of a counted value, for example, which is obtained through the periodical counting up of a counter. Such a counter resets the counted value every time the counted value has reached a maximum value. That is, this type of counter repeatedly uses numerical values within a specific numerical range in a periodical manner (e.g., every two seconds) to express the time. Thus, in case where some malfunction has occurred in the vehicle control system during which the numerical values are counted more than one round, and in case where the determination process is performed as to the validity of the over-one-round counted value, determination error can occur, or moreover, adverse effect may be caused to the real-time control mentioned above.